An "optical fiber" is an elongated glass or plastic filament having a core region surrounded by one or more layers of cladding, with the core having a higher index of refraction than the cladding, so that light introduced at one end of the fiber will be internally reflected for transmission longitudinally within the core channel, to the other end of the fiber. A "fiber optic cable" comprises a sheath surrounding a multiplicity of optical fibers. For further details on optical fibers, see, e.g., U.S. Pat. No. 4,744,631, the disclosure of which is incorporated herein.
In addition to transmitting light in a longitudinal mode, conventional fiber optic cable also transmits light laterally. For data communications, an effort is made to minimize such lateral transmission; however, the lateral illumination is useful for area lighting or spotlighting, such as around swimming pools, walkways, signs, and other safety and decorative accent lighting applications. Attempts have been made in this context to maximize lateral emissions to provide uniform sideways lighting or "glow" over the length of the cable.
Examples of lateral illumination fiber optic cable devices used for safety or decorative illumination purposes are given in U.S. Pat. Nos. 4,933,815 and 4,763,984, the disclosures of which are incorporated herein. Such fiber optic cables or light channels utilize special methods of fabrication, such as the inclusion of actinically-sensitive dyes or other light-scattering materials in the core, to aid in enhancing lateral scattering of the incident light flux.
Other approaches, which do not require specially fabricated fibers, simply bundle large numbers of fibers over each other, either individually or in helically wound groups and cover the same with a clear plastic jacket or cable. Such bundles are not efficient from the aspect of cost and illumination. The central fibers in the cable are wasted due to the fact that the central core of fibers in such cables does not contribute to the visible illumination. Moreover, the central fibers may actually detract from the lateral mode transmissions of the perimetric fibers by causing absorption and attenuation of the light directed toward the center.